This invention relates to a new and novel CRT device for generating a bright red light spot of a type that is particularly useful for projection color television and for information display.
Red light radiation for use in a projection color television generally is produced by the electronic bombardment of red luminescent europium-activated phosphors. The phosphors when excited by electronic bombardment produce a high amount of the desired radiation with a peak at 620 nm. However, a significant amount of radiation is produced in the 580 to 600 nm region and the 620 to 660 nm region in addition to the desired main peak at 610 nm.
As a result of this undesired radiation there is some dilution of the desired radiation. Because of the presence of the undesired radiation blurring of the image may occur when the 610 nm radiation image is brought into focus due to the chromatic aberration of the lens system.
Several methods have been proposed for filtering of undesired radiation from color television tubes. For example, Denki, Japanese Pat. No. 57180859 shows the use of a glass filter plate containing Nd.sub.2 O.sub.3 and a small amount of Cr.sub.2 O.sub.3 or Pr.sub.2 O.sub.3. Seward et al, U.S. Pat. No. 4,086,089 employs glass faceplates for color television tubes, which faceplates function as filters. The faceplates of Seward contain Na.sub.2 O, F, AgHal and SiO.sub.2. The Dutch Octrooi, 144063 shows an salt optical filter employing a lanthanum salt or a lanthanum oxide.
However, the filtering means disclosed in these patents have not been found to be capable of substantially reducing undesired radiation surrounding the desired 610 nm radiation peak without significantly reducing the desired 610 nm radiation peak.